[A4] Catalytic Converter

[Kent McLean]

Ken Witherell wrote:
> Thanks for the advice.  Dealership said they ran the
> diagnostic and the codes turned up the catalytic
> converter.  Dealership is Stammler in Boulder, CO. 
> BTW, as soon as it has gotten cold here, the damn
> light has gone back off?

Someone correct me if I'm wrong, as I may be off base here...
My understanding of the OBD-II diagnostics is that it reports
about the sensors in the system, whether they are working and
within range or not.  What sensor is there that would finger
a catalytic converter as being bad? That is, what does the
OBD-II diagnostics test to determine the cat is bad.

-- 
Kent McLean
'94 100 S Avant, "Moody"
'89 200 TQ, "Bad Puppy" up in smoke